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  • Duration: 01.05.2018 – 31.12.2023
  • : Climate change
  • Research status:  Closed

Hysteresis effects in Bavarian beech forest ecosystems due to climate extremes (HyBBEx)

The beech is the most important deciduous tree species in Bavaria and the key species for a large number of beech forest ecosystems. It offers numerous ecological and economic benefits and is widely accepted as a robust and sustainable component of resilient mixed forests in Bavaria. However, under the conditions of climate change in Bavaria, an increase in the frequency (and extent) of droughts and late frosts is to be expected - climatic extremes to which the beech reacts very sensitively.

HyBBEx investigates the temporal consequences of these climate extremes, so-called hysteresis effects, which can range from special recovery phases to mortality. In addition to important and directly practical questions about the site-specific effects on beech cultivation, the beech cultivation, HyBBEx is primarily concerned with the ecological perspective with a focus on the carbon balance of beech forests - because Hysteresis effects can transform forest ecosystems from carbon sinks to carbon carbon sources and thus directly influence important ecosystem services. influence important ecosystem services.

Reaction of copper beeches in the Bavarian Forest to a late frost event. The upper figure shows the condition on May 3, 2011 before the late frost, the lower figure shows the condition on May 4, 2011 after the late frost. The dots indicate image regions o © Menzel A., Helm R. & Zang C. (2015). Functional Plant Ecology, 6, 110
Taking cores in northern Bavaria. Growth time series from tree ring measurements are a valuable source of data for HyBBEx, as trees store information about their recovery from climate extremes in their ring widths. © Christian Zang

Procedure

At present, we know very little about these hysteresis effects, so that even the most advanced ecosystem models cannot fully predict the recovery of ecosystem productivity after climatic extremes. fully after climatic extremes. Therefore, a realistic process-based projection of the ecosystem functions of forests (and beech forests in particular) is currently is currently not possible. HyBBEx uses an innovative approach that combines data integration, statistical and dynamic modeling as well as model-data fusion in order to make projections of the ecosystem dynamics of Bavarian forest ecosystems through a better understanding of hysteresis hysteresis effects. HyBBEx thus provides basic scientific contributions as well as insights into and ecosystem management that can be directly fed back into forestry practice. directly into forestry practice. Overall, the project aims to make a significant contribution to an improved understanding of the effects of climate change on Bavaria, with direct benefits for the development of regional development of regional adaptation strategies.

Publications

  • Allan Buras, Prof. Dr. Anja Rammig, Prof. Dr. Christian Zang

    • Permissions:  Open Access
    • Permissions:  Peer Reviewed

    The European Forest Condition Monitor: Using Remotely Sensed Forest Greenness to Identify Hot Spots of Forest Decline (2021) Frontiers in Plant Science 12 . DOI: 10.3389/fpls.2021.689220

    Forest decline, in course of climate change, has become a frequently observed phenomenon. Much of the observed decline has been associated with an increasing frequency of climate change induced hotter droughts while decline induced by flooding, late-frost, and storms also play an important role. As a consequence, tree mortality rates have increased across the globe. Despite numerous studies that have assessed forest decline and predisposing factors for tree mortality, we still lack an in-depth understanding of (I) underlying eco-physiological mechanisms, (II) the influence of varying environmental conditions related to soil, competition, and micro-climate, and (III) species-specific strategies to cope with prolonged environmental stress. To deepen our knowledge within this context, studying tree performance within larger networks seems a promising research avenue. Ideally such networks are already established during the actual period of environmental stress. One approach for identifying stressed forests suitable for such monitoring networks is to assess measures related to tree vitality in near real-time across large regions by means of satellite-borne remote sensing. Within this context, we introduce the European Forest Condition monitor (EFCM)—a remote-sensing based, freely available, interactive web information tool. The EFCM depicts forest greenness (as approximated using NDVI from MODIS at a spatial resolution of roughly 5.3 hectares) for the pixel-specific growing season across Europe and consequently allows for guiding research within the context of concurrent forest performance. To allow for inter-temporal comparability and account for pixel-specific features, all observations are set in relation to normalized difference vegetation index (NDVI) records over the monitoring period beginning in 2001. The EFCM provides both a quantile-based and a proportion-based product, thereby allowing for both relative and absolute comparison of forest greenness over the observational record. Based on six specific examples related to spring phenology, drought, late-frost, tree die-back on water-logged soils, an ice storm, and windthrow we exemplify how the EFCM may help identifying hotspots of extraordinary forest greenness. We discuss advantages and limitations when monitoring forest condition at large scales on the basis of moderate resolution remote sensing products to guide users toward an appropriate interpretation.
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  • Prof. Dr. Christian Zang

    Tree growth in a changing climate - From data to model and back again (2024) Vortrag beim Geographischen Seminar, Universität Erlangen, 31.01.2024 .

  • Edurne Martinez del Castillo, Prof. Dr. Christian Zang, Allan Buras, Andrew J. Hacket-Pain, Jan Esper, Roberto Serrano-Notivoli, Claudia Hartl, Robert Weigel, Stefan Klesse, Victor Resco de Rios, Tobias Scharnweber, Isabel Dorado-Liñán, Marieke van der Maaten-Theunissen, Ernst van der Maaten, Alistair S. Jump, Sjepan Mikac, Bat-Enerel Banzragch, Wolfgang Beck, Liam Cavin, Hugues Claessens, Vojtech Čada, Katarina Cufar, Choimaa Dulamsuren, Jozica Gricar, Eustaquio Gil-Pelegrín, Pavel Janda, Marko Kazimirovic, Jürgen Kreyling, Nicolas Latte, Christoph Leuschner, Luis Alberto Longares, Prof. Dr. Annette Menzel, Maks Merala, Renzo Motta, Lena Muffler, Paola Nola, Any Mary Petritan, Ion Catalin Petritan, Peter Prislan, Álvaro Rubio-Cuadadro, Miloš Rydval, Branko Stajič, Miroslav Svoboda, Elvin Toromani, Volodymyr Trotsiuk, Martin Wilmking, Tzvetan Zlatanov, Martin de Luis

    • Permissions:  Open Access
    • Permissions:  Peer Reviewed

    Climate-change-driven growth decline of European beech forests (2022) Communications Biology 5 . DOI: 10.1038/s42003-022-03107-3

    The growth of past, present, and future forests was, is and will be affected by climate variability. This multifaceted relationship has been assessed in several regional studies, but spatially resolved, large-scale analyses are largely missing so far. Here we estimate recent changes in growth of 5800 beech trees (Fagus sylvatica L.) from 324 sites, representing the full geographic and climatic range of species. Future growth trends were predicted considering state-of-the-art climate scenarios. The validated models indicate growth declines across large region of the distribution in recent decades, and project severe future growth declines ranging from −20% to more than −50% by 2090, depending on the region and climate change scenario (i.e. CMIP6 SSP1-2.6 and SSP5-8.5). Forecasted forest productivity losses are most striking towards the southern distribution limit of Fagus sylvatica, in regions where persisting atmospheric high-pressure systems are expected to increase drought severity. The projected 21st century growth changes across Europe indicate serious ecological and economic consequences that require immediate forest adaptation.
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  • Isabel Dorado-Liñán, Blanca Ayarzagüena, F. Babst, Guobao Xu, Luis Gil, Giovanna Battipaglia, Allan Buras, Vojtech Čada, J. Julio Camarero, Liam Cavin, Hugues Claessens, Igor Drobyshev, Balázs Garamszegi, Michael Grabner, Andrew J. Hacket-Pain, Claudia Hartl, Andrea Hevia, Pavel Janda, Alistair S. Jump, Marko Kazimirovic, Srdjan Keren, Jürgen Kreyling, Alexander Land, Nicolas Latte, Tom Levanič, Ernst van der Maaten, Marieke van der Maaten-Theunissen, Elisabet Martínez-Sancho, Prof. Dr. Annette Menzel, Martin Mikoláš, Renzo Motta, Lena Muffler, Paola Nola, Momchil Panayotov, Any Mary Petritan, Ion Catalin Petritan, Ionel Popa, Peter Prislan, Catalin-Constantin Roibu, Miloš Rydval, Raul Sánchez-Salguero, Tobias Scharnweber, Branko Stajič, Miroslav Svoboda, Willy Tegel, Marius Teodosiu, Elvin Toromani, Volodymyr Trotsiuk, Daniel-Ond Turcu, Robert Weigel, Martin Wilmking, Prof. Dr. Christian Zang, Tzvetan Zlatanov, Valerie Trouet

    • Permissions:  Open Access
    • Permissions:  Peer Reviewed

    Jet stream position explains regional anomalies in European beech forest productivity and tree growth (2022) Nature Communications 13 . DOI: 10.1038/s41467-022-29615-8

    The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions.
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  • Paul Bodesheim, F. Babst, David C. Frank, Claudia Hartl, Prof. Dr. Christian Zang, Martin Jung, Markus Reichstein, M. D. Mahecha

    • Permissions:  Open Access
    • Permissions:  Peer Reviewed

    Predicting spatiotemporal variability in radial tree growth at the continental scale with machine learning (2022) Environmental Data Science 1 . DOI: 10.1017/eds.2022.8

    Tree-ring chronologies encode interannual variability in forest growth rates over long time periods from decades to centuries or even millennia. However, each chronology is a highly localized measurement describing conditions at specific sites where wood samples have been collected. The question whether these local growth variabilites are representative for large geographical regions remains an open issue. To overcome the limitations of interpreting a sparse network of sites, we propose an upscaling approach for annual tree-ring indices that approximate forest growth variability and compute gridded data products that generalize the available information for multiple tree genera. Using regression approaches from machine learning, we predict tree-ring indices in space and time based on climate variables, but considering also species range maps as constraints for the upscaling. We compare various prediction strategies in cross-validation experiments to identify the best performing setup. Our estimated maps of tree-ring indices are the first data products that provide a dense view on forest growth variability at the continental level with 0.5° and 0.0083° spatial resolution covering the years 1902–2013. Furthermore, we find that different genera show very variable spatial patterns of anomalies. We have selected Europe as study region and focused on the six most prominent tree genera, but our approach is very generic and can easily be applied elsewhere. Overall, the study shows perspectives but also limitations for reconstructing spatiotemporal dynamics of complex biological processes. The data products are available at https://www.doi.org/10.17871/BACI.248.
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  • . Medienbeitrag, Prof. Dr. Christian Zang

    BR-Rundschau (2019) TV-Beitrag über Forschungen zum Buchensterben in Franken in der BR-Rundschau .

  • Allan Buras, Tom Ovenden, Prof. Dr. Anja Rammig, Prof. Dr. Christian Zang

    • Permissions:  Peer Reviewed

    Refining the standardized growth change method for pointer year detection: Accounting for statistical bias and estimating the deflection period (2022) Dendrochronologia 74 . DOI: 10.1016/j.dendro.2022.125964

    Detecting pointer years in tree-ring data is a central aspect of dendroecology. Pointer years are usually represented by extraordinary secondary tree growth, which is often interpreted as a response to abnormal environmental conditions such as late-frosts or droughts. Objectively identifying pointer years in larger tree-ring networks and relating those to specific climatic conditions will allow for refining our understanding of how trees perform under extreme climate and consequently, under anticipated climate change. Recently, Buras et al. (2020) demonstrated that frequently used pointer-year detection methods were either too sensitive or insensitive for such large scale analyses. In their study, Buras et al. (2020) proposed a novel approach for detecting pointer years – the standardized growth change (SGC) method which outperformed other pointer-year detection methods in pseudopopulation trials. Yet, the authors concluded that SGC could be improved further to account for the inability to detect pointer years following successive growth decline. Under this framework, we here present a refined version of the SGC-method – the bias-adjusted standardized growth change method (BSGC). The methodological adjustment to the SGC approach comprises conflated probabilities derived from standardized growth changes with probabilities derived from a time-step specific global standardization of growth changes. In addition, BSGC allows for estimating the length of the deflection period, i.e. the period before extraordinary growth values have reached normal levels. Application of BSGC to simulated and measured tree-ring data indicated an improved performance in comparison to SGC which allows for the identification of pointer years following years of successive growth decline. Also, deflection period lengths were estimated well and revealed plausible results for an existing tree-ring data set. Based on these validations, BSGC can be considered a further refinement of pointer-year detection, allowing for a more accurate identification and consequently better understanding of the radial growth response of trees to extreme events.
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Recovery of beech forest ecosystems from extreme climatic events

Doctoral candidate
Christopher Leifsson
christopher.leifsson@tum.de
Research focus
Climate change
Time period
01.10.2018 – 31.07.2024
Scientific supervisor HSWT (HSWT)
Prof. Dr. Christian Zang
Facility
Fakultät Wald und Forstwirtschaft

Dynamic modelling of legacy effects of late-frost and drought in European beech forest ecosystems

Doctoral candidate
Benjamin Meyer
ben.meyer@tum.de
Research focus
Climate change
Time period
15.04.2020 – 31.07.2024
Scientific supervisor HSWT (HSWT)
Prof. Dr. Christian Zang
Facility
Fakultät Wald und Forstwirtschaft

Project lead (HSWT)

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